[BrendaAnnD]

The volume problem could as well be in the pre-amp circuit (not on schematic). I would use a scope to check stage gain on the right channel vs. the left.

[morzh]

Didn't Ron say he at some point put the same pre-amp output to both power amps as he was suggested to do and there was still the same difference in volume? That would exclude the pre-amp.

[Ron Ramirez]

Yes, I did - channeled left channel from before volume control to both left and right audio. Right channel still much lower than left.

[morzh]

Well, let's look at those caps. C14, C26 and also C10. I'd hate to think the transformer is involved....(don't think so though).

[morzh]

BTW I do not quite understand the schematic.

What is B+? If it is a rail, how does the driver drive anything? Let alone the fact this same signal comes to bases of Q5 and Q6 and creates different voltages.

Oh, I got it.

Ron, I think you drew the bases going to the wrong places - they should go to Q1 and Q2 collectors respectively. And you have them at B+.
The voltages at the bases and collectors confirm that.

[Mondial]

Looks like there are mistakes in the schematic also. Base of Q6 should connect to collector of Q2, not to the B+ supply as drawn. Same problem on other channel.

As shown, both bases of Q5 and Q6 are shorted together and to supply.

[Ron Ramirez]

Hmmm...I'll double-check either tonight or this weekend. A bit frustrating, not having an actual 4400 schematic.

[morzh]

You do not have to double-check, if it were the case you would not hear anything and your transformer would simply be placed across a constant B+ voltage.
It is a drawing mistake, I can guarantee you.

[Ron Ramirez]

No, I meant double-check the schematic I had to modify in an attempt to match the 4400 audio circuit.

Oh, and regarding the interstage transformer, it has good continuity, for what that's worth.

[morzh]

Oh...I did not mean continuity - otherwise it would not play. I meant some sort of a turn short (it would barely play or not play though....depends on parasitics of the transformer).

Your B+ from the measurements is about 31-32V, right?

[Ron Ramirez]

Well, I found the mistake on my schematic and corrected it below.

[Image: http://www.philcoradio.com/images/phorum...p_Rev1.jpg]

Yes, boys and girls, B+ is fed through R19 and R20, both 8.2K 1/2 watt resistors, to the collectors of Q1 and Q2, and to the bases of Q5 and Q6. The same source also has a 120 ohm, 2 watt resistor (added in the revised schematic above) which feeds the emitters of Q5 and Q6 through 560 ohm, 3 watt resistors.

It will take some time to trace out the power supply and convert it into schematic form. But I can assure you that from the volume controls through the audio circuit, including the power supply lines, this schematic is now correct. The audio amplifier control board above the audio output circuitry may or may not match the 4400 - I haven't gone that far yet.

Now, I'll go back and measure the B+ source (labeled To Power Supply in the revised schematic above) to see what that voltage is, just for fun.

[Ron Ramirez]

I went back to the bench and ran several more tests, took more voltage readings, and pulled out the signal tracer.

I had set aside the original TR-110B output transistors as they seemed to be OK after testing. This was before I cleaned the switches of my "new" transistor tester with DeoxIT. Well, I tested them again tonight - yes, they are good! So, back in they went. This raised the previous voltage readings of 19.6 and 19.7 volts to above 22 volts.

For some reason, I felt suspicious of the GE-3 driver I had installed in place of the bad original TR35144, so I installed a NOS 40626 Ge transistor (same specs as NTE121/GE-3/GE-16/TR35144). No change, right channel was still lower than the left.

I measured 29.99 volts at B+ (the common point where my most recent revised schematic states To Power Supply).

I replaced C14 and C26 with the only things I had - a 4.7 uF, 450V cap for C14 and a 100 uF, 100V cap for C26. No change.

Then I hooked up the signal tracer. This was quite revealing.

The sound in the right channel just before the volume control was louder than that of the left. This was because I had the balance control set to favor the right channel as I listened to a local FM station while doing my tests.

Now, bringing the tracer down through the audio output circuitry, I compared the left channel to the right by using the probe on the base of Q2, then the base of Q1, then the collector of Q2, then the collector of Q1.

I think I have found the problem.

The sound was louder at the collector of Q1 (left channel) than at the collector of Q2 (right channel).

The sound was equal, more or less, at the base of Q2 and at the base of Q1.

When I set this chassis on the bench, I found that someone had replaced Q2 with something other than a 2N2924. I did not have a 2N2924 on hand. So...I stuck in a transistor equivalent to an NTE123.

I think this was my big mistake.

Oh, I restored audio in the right channel, all right, but not to full specs. And I had been going around in circles ever since.

2N2924 transistors are 59 cents at Mouser.

So...since I need to order some electrolytics anyway, I'll also order a genuine 2N2924. We shall then see how the right channel performs. I will go ahead and replace all power supply and audio output electrolytics while I'm at it.

Edit: I now see that 2N2924 (NTE85) has a much higher hFE (min. 100) than the NTE123 (hFE min. 30). So it now makes sense to me that using an NTE123 equivalent was a poor choice. Kind of like trying to substitute a 27 for a 6J5.

[Mondial]

Ron, you might also check the values of R22 and R48 and compare them to the corresponding ones R21 and R47 on the other channel. Each pair of resistors form the negative feedback network which determines the overall gain of the amp. If the 100 ohm resistor has gone up in value it will decrease the gain of the amp. Approx overall voltage gain is 100 + 2700 / 100 = 28.

Because of the negative feedback, minor differences in the hFE of the input transistor will have only a small effect on overall gain.

[BrendaAnnD]

A.G. Tannenbaum appears to have the service manual for this receiver:

http://www.agtannenbaum.com/f_cat.htm

[Ron Ramirez]

Hey, that's great! Thanks! I'll be contacting Tannenbaum soon...and ordering a lot of lower voltage, high temp electrolytics from Mouser soon...and a 2N2924...

Mondial, I will also check the values of those resistors to be sure - thanks.